Telephone system



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Patented May 27, 1947 UNITED STATES 'PATENT jFEICI'.

TELEPHONE .SYSTEM Burton McKim, East Orange, N. il., :assigner to BellTelephone Laboratoriesnoorporated,New York, N. Y., a .corporation of NewYork Application August 18, 1944, Serial N o. @550,071

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21 Claims.

This invention relates to telephone systems and more particularly tosuch systems with four-wire transmission circuits.

The object of the presentinvention resides in the improvement offacilities `4for controlling transmission quality over trunks and linesfrom a manually operable switchboard.

A feature iof the invention consists in amanually operable switchboardhaving cord circuits with multicontact plugs for connecting Ythe twochannels of one jack terminating vfour-wire trunk tothe two channels ofIanother jack terminating 'four-wire trunk.

Another and related feature consists in mechanism in this manually-operable switchboard for registering the transmission characteristicsAof the line and trunks connected to a `cord circuit for automaticallyinserting voice amplifying repeaters in each of the two transmissionchannels or disconnecting voice amplifying repeaters from each of thetwo transmission channels, according to the trunk -and linecharacteristics Aindicated in the switchboard mechanism.

Another and related feature consists in repeated use of trunks anda lineconnected to vone twin plug of a cord circuit `without removing the plugfrom vsaid trunk Yconnection and connecting the other plug of the cordcircuit to a plurality of different trunks -to diiferent lines withmeans in said switchboard tcregister the characteristics of each 'trunkconnection and automatically insert voice amplifying repeaters in thetransmission channels or remove voice amplifying repeaters from thetransmission channels, which were previously inserted therein.

The foregoingand other -features of the inven- -tion will bedescribedmore fully in the following specification which should be ntaken inconnection with the accompanying drawings and appended claims.

Referring to the drawings:

Figs. 6, 7, 8 and 9 illustrate a manually operable toll switchboard;

Fig. 1 .illustrates a four-wire outgoing trunk to a toll oce over a lowloss toll line;

rFigs. 2 and 12feach-illustrates -afour-wire outgoing trunk to a tolloiice over a high loss toll line;

Figs. 3 and 13 illustrate selectable voice amplifying repeaters;

Figs. 5 .and 10 illustrate special four-wire trunks outgoing from thetoll-switchboard;

Figs. 4 and 11 diagrammatically `illustrate senders and markersand-cross bar switches operable under the control of the switchboard for2 selecting vthe outgoing 4trunks land ifor connecting them to thespecial trunks, Figsf5 and 10; Y

Fig. 14 illustrates an incoming trunk Afrom either a high loss toll line-or la low loss -toll 'line and Adiagrammatically illustrates ya senderIIoperable over said lines;

Fig. l5 illustrates a special trunk incoming vto lthe toll switchboardfrom the incoming trunk, Fig. A14, and diagrammatically -illustrates amarker and Ycross `bar switch for connecting the trunk, Fig. 1'4 tothetrunk, Fig. 15;

Figs. '17, 18 and 19 illustrate Vfour-wire trunks incoming 1to andoutgoing from the manually operable toll switchboard, Figs. 6,47, `8 andV9; and

Figs. 16 and-20 -show the mannerof assembling the drawings toillust-rate the invention.

T-he sender diagrammatically disclosed herein vand the manner vofoperating this sender maybe as disclosed in the copending application ofB. McKim `and 0. 'Myers Seria-l No. 550,070, filed August 18,1944,whichissued asPatent-No. 2,382,- 893 Yon August 14, 1945. Themarker, link connector, and -the `trunk block relaysdiagrammatically*disclosed herein maybe ofthe typedisclosed in Patent2,236,246 to'G. V. King, J. B.`Mc Kim andO. Myers, March 25, 1941, andPatent :2,293,191 A. J. Busch and F. J. Scudder, August 18, `1942. Themarker-connector maybe of the type disclosedin Patent 2,241,016 to G. V.-King, F. A. Korn and R. K. -McAlp-ine, May -6, 1941.

General description It is shown in Patent lNo. 2,382g8931toMcKim andMyers, that there are occasions when .toll -tr-unk groups outgoing froman automatic toll switching ofce become Aoverloadedeither for a shortYduration -of time 'or for several hours. Under such conditions callsfrom ynearby ordis- 'tant toll ofces encounter delay in vobtaining anidletrunkin these-groupsfor completingftool telephone connections.In-order to 'facilitate thecom.- pleting of toll connections over trunksin .such groups, a call vorder `switchboard is provided .to whichincoming calls :may be routed which have encountered delay in obtainingian idle toll trunk to a 'desired destination. The call order switch-'board has a number of operators positions :for handling ydelayed callsand announcing the amountof delay expected in completing-calls to tolltrunks in groups to particular oiiices. This switchboard is supervisedby a supervisors7 Operator who in combination witha` grouper persons,observes signals Awhich .indicate the Aoverloading of trunk groups whichifseverely overloaded are -made unavailable to incoming calls from otheroffices and are made only available to the operators in the call orderswitchboard. A special arrangement is provided for making groups oftrunks unavailable to incoming calls so that the calling operator isimmediately appraised of the delay anticipated in obtaining an idletrunk for completing the desired connection. A ticket is written by acall order board operator covering the information for each call,including the originating toll operators number and the trunk connectiondesired and these tickets are led or stacked in a particular order sothat the delayed calls may be completed substantially in the orderreceived. The responsibility of completing these delayed telephoneconnections then rests upon the call order switchboard operators insteadof the various calling operators from other toll ofces and the time ofthese calling operators which would otherwise be required in makingnumerous attempts to complete the delayed connections is saved sinceonly one call to the call order board operator is necessary.

Each group of toll trunks outgoing to other oices has one or more overowtrunks associated therewith which are connected by automaticallyoperable mechanisms, along with the trunks of the group, with a trunktesting unit ,when the code of this trunk group is transmitted to theautomatic switching office. The testing unit tests the trunks in theoutgoing group of trunks and when no idle trunk is found it tests theoverow trunks and if an idle overflow trunk is found the incoming trunkis automatically routed thereto. The overflow trunk has two types ofsignals, one which ashes an indication over the incoming trunk that alltrunks in the group are busy. This signal may be altered to a differenthashing signal if a trunk in the group becomes idle while the callingoperator holds the incoming linehoping to receive this second iiashingsignal. Whenever a call is routed to an overflow trunk, a signal isoperated which may be observed by the supervisory staff. If the calling,operator does not receive a second flash after a given time, theconnection is released and this operator then has the choice of makinganother attempt toY obtain an idle trunk in this group a few minuteslater or she may pulse a circuit request call which requires a specialcode to connectjher through the mechanism of the automatic switchingomc@ with a trunk extending to the call order switchboard. Each callorder switchboard position has a cord and telephone circuit forconnection to this trunk and also has mean's to observe whether there isan idle trunk inthe desired outgoing group. If the group is overloaded,this operator refers to a bulletin handed to her by the supervisorygroup. This bulletin posts all groups which are overloaded and on whichthere is a time delay in completing calls. The call order board operatoradvises the calling operator the condition of the group and writes aticket to complete the call later if it cannot be immediately completed.

The supervisory stan" observes the overow signais if they-are constantlyoperated and investigates the number of circuit request calls for whichtickets have been written by the call order board operators for anygroup of trunks which are gaining in demand. If the trunks of a groupare constantly busy and a given number of circuit request tickets havebeen written, a delay announcing circuit is patched to the overow trunksof the group and thereafter the calling incoming trunks which are routedto an 4 overflow circuit receive an announcement of the time period ofdelay in completing toll connections to the trunks of this group,instead of receiving the aforementioned flashing signals. The patchingof the overflow trunks of a trunk group to the delay quotation circuitalso operates mechanism to automatically make this group of trunksunavailable to incoming calls, even though there are idle trunks in thegroup. As these trunks become idle they are taken for use by the callorder board operators for completing circuit request calls from ticketspreviously written.

The circuits and mechanisms disclosed herein deal with the completion ofthe toll telephone calls by the call order board operators and automaticsignaling arrangements between trunks yand the operators positionmechanism for inserting and removing voice amplifying repeatersaccording to characteristics required for good transmission overlow-loss and high-loss toll lines. The low-loss toll line and the trunkmechanism with which it is connected will herein be called a short tollline and is one in which the loss because of resistance of the lineconductors and other mechanisms connected therewith is low enough toprovide good transmission characteristics. A high-loss toll line and thetrunk mechanism with which it is connected Will herein be called a longline andis one having a line and associated mechanism of sucientresistance to require voice amplifying repeaters to give itsubstantially the equivalent transmission of the low-loss or short tollline. Under normal conditions in the automatic switching toll oiice, thetrunks connected to long and short lines operate mechanism in the senderand marker which are automatically connected thereto to indicate to themarker where and when a voice amplifying repeater is required and themarker may operate mechanism in the selected outgoing trunk which causesthe insertion of repeaters in the transmission channels. These functionsare somewhat different when calls are completed through the call orderboard, since the same trunk outgoing or incoming may be used for anumber of telephone connections.

The arrangement disclosed in this application includes an incomingtrunk, Fig. 14, which may be incoming over a short toll line from anearby CLR toll oiice '|460 or over a long toll line to a toll oice in adistant city lii, which assumes that the toll onice i400 may be in twodiii'erent locations in order to economize in the drawings of thisapplication. The trunk, Fig. 14, may be used for incoming calls forcompleting toll telephone connections over outgoing trunks, as describedin the aforementioned Patent 2,382,893, to M cKim and Myers, but the useherein described will be for making circuit request calls to the callorder switchboard. This assumes that a call was previously made by anoperator in oflice l who was advised by signals that all of the outgoingtrunks to the desired office were busy or by an announcement that therewould be a given delay in obtaining an outgoing trunk to complete theVconnection. The operator in oice l may make a circuit request call bysending circuit request code pulses over the incoming toll line whichare recorded by a sender and marker and the marker selects an idle trunkin a group of circuit request trunks shown in Fig. 15 which terminatesin twin jacks and a lamp in the call order switchboard. As explained inthe aforementioned patent, a call from a distant of- Viice over a longtoll line is automatically routed

